Advanced Features Of High Speed Digital I/O Devices: Double Data Rate

As clock speeds and data rates continue to increase, designers of digital integrated circuits are creating new ways to maximize the rate of data being sent into and out of digital devices. One such method is known as double data rate (DDR). With single data rate (SDR) devices, data is latched on either the rising or falling edges of the sample clock. A DDR device latches data on both the rising and falling edges of the sample clock, effectively doubling the data transfer rate without increasing the clock speed. This application note describes DDR and its use with National Instruments digital waveform generator/analyzer devices.